1. Field of the Invention
The present invention relates to composite materials with elevated electric field induced strain levels, elevated dielectric constants, and having flexible mechanical properties. The materials of the invention comprise a polymer matrix and high dielectric constant organic material.
2. Description of the Prior Art
Because of their many attractive features such as light weight, high mechanical flexibility, and conformability, electroactive polymers are of great interest for a broad range of applications such as electromechanical and dielectric devices. On the other hand, compared with ceramic materials, the electroactive properties of polymers, such as the dielectric constant and electromechanical response, are not very high. In the past several decades, there has been a great deal of effort to develop polymers with improved functional properties. One of the focuses of these research and development efforts is to raise the dielectric constant of polymers substantially. In addition to applications directly related to capacitors and charge storage devices, a high dielectric constant polymer is also required for high electromechanical responses. The reason behind this is that in the electromechanical transformation process, the mechanical energy output of an electroactive material can't exceed the input electric energy due to the principle of energy conservation. The input electric energy is directly proportional to the dielectric constant of the material and also the square of the applied field. Therefore, in order to develop high performance electroactive polymers for electromechanical applications, one of the key issues is how to substantially raise the dielectric constant of the polymer.
Recently, by making use of high energy electron irradiation, it has been shown that the room temperature dielectric constant of poly(vinylidene-trifluoroethylene) copolymer P(VDF-TrFE) can be increased to about 50, a marked improvement compared with the current available polymers. Elevated dielectric constant PVDF-based terpolymer materials are also developed. However, how to raise the dielectric constant to much higher level without stiffening the polymers is still a challenge. For example, using high dielectric constant ceramics as the filler, the room temperature dielectric constant of the so-called 0-3 composites (ceramic powder polymer matrix composites) can reach 300. One of the consequences of this ceramic filling process to the 0-3 composites is to increase the elastic modulus of the composites significantly above that of the polymer matrix. It is an objective of the present invention to develop alternative 0-3 composite approaches to achieve high dielectric constant while maintain the high flexibility of the matrix. The present invention shows that by making use of the organic solids which possess high dielectric permittivity through the mechanism of nomadic polarization as the fillers, at room temperature and 100 Hz, a composite material with dielectric constant more 1,000 and dielectric loss less than 0.5 can be realized. The composite film is also mechanically flexible with the elastic modulus nearly the same as that of the polymer matrix. In addition, the composite films which elastic modulus is 0.6 GPa also exhibit high strain (˜2%) under an electric field of 13 MV/m, a marked improvement compared with other electroactive polymers.
Accordingly, it is an object of the invention to provide polymer matrix materials that exhibit elevated room temperature dielectric constants.
It is another object of the invention to provide polymer matrix materials comprising high dielectric constant material.
It is yet another object of the invention to provide polymer matrix materials having desirable dielectric properties that have mechanical properties similar to their polymer matrix.
These and other objects and advantages of the present invention and equivalents thereof, are achieved by composites useful for electrical applications.